Superconductive junction, superconducting apparatus, method of manufacturing superconducting junction and control method of superconducting junction

ABSTRACT

A superconducting junction comprises: a first layer and a second layer of superconducting material; a tunneling layer of insulating material disposed between the first layer and the second layer of the superconducting material; and a layer of thermally conducting, non-superconducting material disposed between the first layer and the second layer of the superconducting material, the non-superconducting layer being in contact with either the first layer or the second layer of superconducting material.

This application is a continuation of U.S. application Ser. No.16/474,789 filed Jun. 28, 2019, which is the U.S. national phase ofInternational Application No. PCT/FI2017/050948 filed Dec. 28, 2017,which designated the U.S. and claims priority to Finnish PatentApplication No. 20166053 filed Dec. 30, 2016, the entire contents ofeach of which are hereby incorporated by reference.

FIELD

The invention relates to a superconductive junction, superconductingapparatus, a method of manufacturing a superconducting junction and acontrol method of a superconducting junction.

BACKGROUND

Superconducting-Insulator-Superconducting (S-I-S) junctions are alsocalled Josephson junctions. Measurement devices utilizing the S-I-Sjunctions as detectors suffer from low-frequency noise, which is atleast partially related with temperature fluctuations. In prior art, anarea of the Josephson junction has been made large, so that fluctuationswould average out. The large-area of the Josephson junction, however, isprone to the problem of flux-trapping.

The S-I-S junctions are applied in SQUID magnetometers which may operatewith presence of high transient magnetic field (as in low-field MagneticResonance Imaging). The S-I-S junctions are sometimes protected againstdisturbance during the magnetic transient, by heating the SQUID into anon-superconducting state because the high transient magnetic field maycause the flux traps which may persist for seconds to hours insuperconducting temperatures. Fast recovery from the non-superconductingstate to the superconducting state is, however, slow which is why theprotection on the basis of heating is impractical with currentlyavailable means.

Hence, there is a need to improve the protection against or alleviationof the temperature related disturbances of the measurement devicesutilizing the superconducting S-I-S junctions.

BRIEF DESCRIPTION

The present invention seeks to provide an improvement for devicesutilizing S-I-S junctions. According to an aspect of the presentinvention, there is provided a superconducting junction as specified inclaim 1.

According to another aspect of the present invention, there is provideda superconducting apparatus in claim 4.

According to another aspect of the present invention, there is provideda manufacturing method of a superconducting junction in claim 14.

According to another aspect of the present invention, there is provideda control method of a superconducting junction in claim 15.

The invention has advantages. The superconducting junction can betemperature stabilized or its temperature can be controllably variedbetween superconducting state and non-superconducting state in a fastmanner.

LIST OF DRAWINGS

Example embodiments of the present invention are described below, by wayof example only, with reference to the accompanying drawings, in which

FIG. 1A illustrates an example of a layered structure of asuperconducting component from side;

FIG. 1B illustrates an example of a layered structure of asuperconducting component from above;

FIG. 1C illustrates an example of a layer of the non-superconductingmaterial within the superconducting junction;

FIG. 1D illustrates another example of a layer of thenon-superconducting material within the superconducting junction;

FIG. 1E illustrates still another example of a layer of thenon-superconducting material within the superconducting junction;

FIG. 2 illustrates an example of a temperature controlling element forthe superconducting junction;

FIG. 3 illustrates an example of a temperature stabilizer for thesuperconducting junction;

FIG. 4 illustrates an example of a heating and cooling systems for thesuperconducting junction;

FIG. 5 illustrates an example of a magnetic resonance imaging machine;

FIG. 6 illustrates an example of a magnetoencephalography machine;

FIG. 7 illustrates an example of periods of heating and the heatedsuperconducting junction;

FIG. 8A illustrates an example of temperature fluctuation within atemperature range enabling a superconducting state;

FIG. 8B illustrates example temperature fluctuation inside and outside asuperconducting state;

FIG. 9 illustrates an example of characteristics of a superconductingjunction in liquid helium;

FIG. 10 illustrates an example of a processing unit with at least oneprocessor and at least one memory;

FIG. 11 illustrates an example of a flow chart of a manufacturing methodof a superconducting junction; and

FIG. 12 illustrates an example of a flow chart of a control method of asuperconducting junction.

DESCRIPTION OF EMBODIMENTS

The following embodiments are only examples. Although the specificationmay refer to “an” embodiment in several locations, this does notnecessarily mean that each such reference is to the same embodiment(s),or that the feature only applies to a single embodiment. Single featuresof different embodiments may also be combined to provide otherembodiments. Furthermore, words “comprising” and “including” should beunderstood as not limiting the described embodiments to consist of onlythose features that have been mentioned and such embodiments may containalso features/structures that have not been specifically mentioned.

It should be noted that while Figures illustrate various embodiments,they are simplified diagrams that only show some structures and/orfunctional entities. The connections shown in the Figures may refer tological or physical connections. It is apparent to a person skilled inthe art that the described apparatus may also comprise other functionsand structures than those described in Figures and text. It should beappreciated that details of some functions, structures, and thesignalling used for measurement and/or controlling are irrelevant to theactual invention. Therefore, they need not be discussed in more detailhere.

FIGS. 1A and 1B illustrate an example of a layered superconductingcomponent 10. FIG. 1A shows a cross sectional view of thesuperconducting component 10. FIG. 1B shows a top view of thesuperconducting component 10 downwards from the level marked with adouble-dotted dashed line. In FIG. 1B, only layers 102, 104, 106 and 108are shown for simplicity. Heating and cooling systems 400, 402 shown inFIG. 4 are used to heat and cool the superconducting junction 100 to atemperature above and/or below a superconducting temperature fromoutside of the superconducting junction 100. The cooling system 402 isalso typically outside the superconducting component 10.

The superconducting junction 100 thus comprises the first layer 104 andthe second layer 106 of superconducting material, a tunneling layer 108of insulating material disposed between the first layer 104 and thesecond layer 106 of the superconducting material, and the layer 102 ofthermally conducting, non-superconducting material disposed between thefirst layer 104 and the second layer 106 of the superconductingmaterial, the non-superconducting layer 102 being in contact with eitherthe first layer 104 or the second layer 106 of superconducting material.

The superconducting component comprises a superconducting junction 100which is a new kind of Superconducting-Insulator-Superconducting (S-I-S)junction or a new kind of Josephson junction. The first layer 104 ofsuperconducting material and the second layer 106 of superconductingmaterial may overlap each other at an area A of the superconductingjunction 100. The first superconducting layer 104 of the superconductingmaterial and the second layer 106 of the superconducting material areelectrically superconducting in a temperature low enough. The firstsuperconducting layer 104 of the superconducting material and the secondlayer 106 of the superconducting material may provide electric contactsto the superconducting junction 100, and enable an electric current flowto and/or from the superconducting junction 100. The sizes of areas ofthe superconducting junction 100 and the first superconducting layer 104may be different from what is drawn in FIGS. 1A and 1B.

The first and second layers 104, 106 of superconducting material maycomprise metal, for example. The first and second layers 104, 106 ofsuperconducting material niobium, magnesium diboride and/or aluminum,for example. The thicknesses of the first superconducting layer 104 ofthe superconducting material and the second layer 106 of thesuperconducting material may be corresponding to those as in the priorart.

The tunneling layer 108 of insulating material may be an oxide layersuch as aluminum oxide, magnesium oxide, niobisiliside or the like, forexample. The tunneling layer 108 of insulating material is at least atthe superconducting junction 100 but it may also extend to thesurroundings of the superconducting junction 100. The thickness andmaterial of the tunneling layer 108 may be corresponding to those as inthe prior art.

The layer 102 of non-superconducting material which may poses a propertyof a superconducting proximity effect. The layer 102 ofnon-superconducting material is a thermal conductor for thermal controlof the superconducting junction 102 within the superconducting junction100. The layer 102 of the non-superconducting material may be in contactwith either of the first layer 104 of the superconducting material orthe second layer 106 of the superconducting material. That is, the layer102 of the non-superconducting material may be between the first layer104 of the superconducting material and the tunneling layer 108 orbetween the second layer 106 of the superconducting material and thetunneling layer 108.

The superconducting proximity effect or Holm-Meissner effect refers to aphenomenon where superconductivity is present in a basicallynon-superconducting material layer such as the layer 102 which issandwiched between two superconducting material layers i.e. the firstand second layers 104, 106. The non-superconducting material layer 102is typically rather thin, from nanometers to micrometers. The thicknessof the non-superconducting material layer 102 which becomessuperconductive between the superconducting material layers 104, 106 onthe basis of the superconducting proximity effect depends on thematerial, for example.

Metals typically have a superconducting proximity effect. Thenon-superconducting layer 102 may include or may be made of titaniumtungsten alloy (TiW), copper or the like, for example. Thesuperconducting proximity effect may also be present in non-metals. Anexample of a non-metal with the superconducting proximity effect isgraphene without limiting to this example. Thus, the non-superconductinglayer 102 may include or may be made of graphene, for instance.

In embodiments examples of which are shown in FIGS. 1C, 1D and 1E, anarea B of the layer 102 of the non-superconducting material within thesuperconducting junction 100 is smaller than a superconducting area A ofthe superconducting junction 100. The area B of the layer 102 of thenon-superconducting material may have a different shape than the area Aof the superconducting junction 100. In FIG. 1C the area B of the layer102 of the non-superconducting material has a shape of a rectangle andthe area A of the superconducting junction 100 has a shape of a circle.In FIG. 1D the area B of the layer 102 of the non-superconductingmaterial has a shape of an annulus and the area A of the superconductingjunction 100 has a shape of a circle. The annular area B leads to astructure where the central area of the superconducting junction 100lacks the non-superconducting material. However, the non-superconductingmaterial still exists within the area A of the superconducting junction100.

FIGS. 1C and 1D illustrates examples where the layer 102 of thenon-superconducting material is connected to a temperature controllingelement 200 (shown in FIG. 2 ) at more than one side.

FIG. 1E illustrates an example where the layer 102 of thenon-superconducting material is connected to the temperature controllingelement 200 at one side. In FIG. 1E, the layer 102 of thenon-superconducting material extends outside the superconductingjunction 100 only at one side, and on the opposite side the layer 102 ofthe non-superconducting material ends within the area A of thesuperconducting junction 100.

The superconducting junction 100 may comprise also other layers, such ashatched layers in FIG. 1A for example, but they are not explained andthey should be understood as not limiting the described embodiments.Some of said other layers may comprise silicon dioxide, for example.

FIG. 2 illustrates an example of a superconducting apparatus, which mayrefer to the superconducting component 10 or the like, and which maycomprise the superconducting junction 100. Additionally, thesuperconducting apparatus may comprise a temperature controlling element200 outside of the superconducting junction 100. In an embodiment, thetemperature controlling element 200 may be outside the superconductingcomponent 10. In an embodiment, the temperature controlling element 200may be inside the superconducting component 10.

The temperature controlling element 200 is coupled with the layer 102 ofthe non-superconducting material for controlling the temperature of thesuperconducting junction 100. In an embodiment, at least one thermalconductor 202 coupling the layer 102 of the non-superconducting materialwithin the superconducting junction 100 and the temperature controllingelement 200 together may include the non-superconducting material of thelayer 102. In an embodiment, the thermal conductor 202 coupling thelayer 102 of the non-superconducting material within the superconductingjunction 100 and the temperature controlling element 200 together mayinclude non-superconducting material different from that of the layer102. In general, the thermal conductor 202 may be metal. The thermalconductor 202 may be coupled with the layer 102 of thenon-superconducting material within the superconducting junction 100 atleast at one side. FIG. 2 shows two thermal conductors 202 where one ofthe thermal conductors 202 may or may not be present and that is why itis drawn with a dashed line.

In an embodiment, the thermal conductor 202 may be realized by lettingthe non-superconducting material of the layer 102 of extend from thesuperconducting junction 100 outside up to the temperature controllingelement 200.

In an embodiment, the temperature controlling element 200 may comprise astabilizer 300 which has a higher heat capacity than that of the layer102 of the non-superconducting material at the superconducting junction100. The heat capacity C is measured by dividing heat (energy) Q bytemperature change ΔT, i.e. C=Q/ΔT. The stabilizer 300 may be set in adesired temperature for keeping temperature of the layer 102 of thenon-superconducting material, which is operationally coupled with thestabilizer 300, within a first temperature range 800 (see FIG. 8A) andfor keeping a temperature of the superconducting junction 100 within asecond temperature range 802 (see FIG. 8A, 8B). The second temperaturerange 802 depends on the first temperature range 800 and in practicethey can be considered the same. Irrespective of breadths of the firstand second temperature ranges, temperature fluctuations at thesuperconducting junction 100 can be limited or stabilized on the basisof thermal inertia of the stabilizer 300 and good thermal conductivityof the at least one thermal conductor 202. The first and secondtemperature ranges are desired temperature ranges which can bedetermined by a person skilled in the art on the basis of requirementsand materials.

The thermal conductance of the thermal conductor 202 transmits the heatfrom the layer 102 of the non-superconducting material to the stabilizer300 or from the stabilizer 300 to the thermal conductor 202. The layer102 of the non-superconducting material, in turn, transmits heat fromthe superconducting junction 100 the thermal conductor 202 or from thethermal conductor 202 to the superconducting junction 100.

The first desired temperature range and the second desired temperaturerange may be different. The first desired temperature range and thesecond desired temperature range may be overlapping at least partially.The first desired temperature range and the second desired temperaturerange may be the same. In an embodiment, the stabilizer 300 is set in adesired temperature for keeping a temperature of the layer 102 of thenon-superconducting material constant and for keeping a temperature ofthe superconducting junction 100 constant. The constant temperature ofthe layer 102 of the non-superconducting material and thesuperconducting junction 100 may be different. The constant temperatureof the layer 102 of the non-superconducting material and thesuperconducting junction 100 may be the same.

For example, SQUID magnetometers suffer from low-frequency noise, whichis at least partially related with temperature fluctuations. The gapvoltage and other properties of the superconducting junction 100 dependon its temperature, and the properties may be affected by localtemperature fluctuations. Sometimes it is useful to control the junctionparameters, too, by intentional temperature changes. Thermal control ofthe Josephson junctions is difficult, however, because they aretypically buried inside thermally-isolating insulation layers, andbecause superconducting metal itself is a poor heat conductor. The useof S-N(S)-I-S junctions in SQUIDs instead of the traditional S-I-Sjunctions, where N(S) denotes the layer 102 of the non-superconductingmaterial driven superconductive by the proximity effect in the vicinityof the superconductive electrodes 104, 106, eliminates or alleviates thetemperature fluctuations of the superconducting junction 100. The layer102 of the non-superconducting material, which may be of normal metal orother heat conductor, provides a well-conducting thermal link coupledwith the stabilizer 300, which allows temperature control of thesuperconducting junction 100.

In low-field MRI (Magnetic Resonance Imaging), the superconductinglayers 104, 106 of the superconducting junction 100 can be kept narrow,which alleviate flux-trapping, and still the low-frequency noise may beeliminated or kept moderate with the temperature stabilization.

In an embodiment a simplified example of which is illustrated in FIG. 4, the temperature controlling element 200 may comprise a heater 400which may provide heating power to heat, for a first period 700 of time(see FIG. 7 ), the layer 102 of the non-superconducting material to atemperature higher than a highest temperature at which thesuperconducting junction 100 is superconducting. The layer 102 of thenon-superconducting material transfers the heat to the firstsuperconducting layer 104 and the second superconducting layer 106 whichcauses their temperature to rise. The rise in temperature, in turn,causes the first superconducting layer 104 and the secondsuperconducting layer 106 to become non-superconducting for a secondperiod 702 (see FIG. 7 ). The heater 400 may output more heat energy forthe superconducting junction 102 during the first period 700 than isconsumed by heat loss in the one or more thermal conductors 202 and thecooling system 402. The cryogenic cooling of the cooling system 402 maybe based on liquid helium, for example. The liquid helium may surroundthe component 10 but is not necessarily in direct contact with thesuperconducting junction 100. The heater 400 and the stabilizer 300 maybe used alternatively or together for having a proper thermal control ofthe superconducting junction 100.

The first and second periods 700, 702 may be the same but because of apotential difference in thermal inertias between the superconductivejunction 100 and the layer 102 of the non-superconductive material,there may a temporal difference. The first and second periods 700, 702may be temporally overlapping. The superconducting junction 100 issuperconductive outside the second period 702 on the basis of coolingpower from a cooling system 402 outside the superconductive junction100.

Because the volume of the layer 102 of the non-superconducting materialis much smaller in the superconducting junction 100 than a wholedetector or the component 10 and/or because the thermal contact of thelayer 102 to the junction 100 is good, the superconducting junction 100can effectively and quickly be heated up and cooled down. In the priorart, the whole detector or the component 10, which is a large objectcompared to the superconducting junction 100 alone, is heated up and ittakes a long time to cool it down. By controlling the temperature of thesuperconducting junction 100 from within the junction directs theheating and cooling to an essential and small volume without changingtemperatures in operationally unnecessary areas in the detector or thecomponent 10. This reduces the thermal inertia and quickens both theheating and cooling of the superconducting junction 100. In this manner,it is possible, depending on the size of the superconducting junction100, to switch between the superconducting state and thenon-superconducting state of the junction 100 in a range 1 ms to 50 msin the fastest manner. By making the superconducting junction 100 verysmall, the state of the superconducting junction 100 may be changed fromsuperconducting to non-superconducting or vice versa faster than 1 ms.Naturally, the state of the superconducting junction 100 may also bechanged slower than the fastest times above in a controllably manner.

In an embodiment, the temperature controlling element 200 may compriseor may operationally be coupled with a thermometer 404 which may measurea temperature of the layer 102 of non-superconducting material. Thetemperature controlling element 200 may receive information about themeasured temperature from the thermometer 404 and increase, keep ordecrease the heating power of the heater 400 in response to theinformation about the measured temperature. The state of thesuperconducting junction 100 may also be changed in a controllablymanner by following the temperature data of the thermometer 404.

In general, the area A of the superconducting junction 100 can betemperature-stabilized either by a large thermal body 300 or using anactive temperature control provided by the heater 400 and thethermometer 404.

FIG. 5 illustrates an example of an MRI (Magnetic Resonance Imaging)machine. The MRI machine, which may be combined withmagnetoencephalography technology, and its use, per se, are known by aperson skilled in the art and that is why they don't need to beexplained in detail. The prepolarization field may be about 0.1 T andthe working field may be about 100 μT, for example. The MRI machine mayhave a closed or open tube. A transmitter-receiver 500 has anelectro-magnet which outputs at least one magnetic pulse to an object502 for one measurement. The transmitter-receiver 500 also has atransmitter which transmits varying magnetic field, which may be inkilohertz range. Both the magnetic pulses and the varying magnetic fieldare transmitted under the control of a processing unit 504 which may bea computer. The processing unit 504, in turn, may be controlled by adoctor or other professional staff using a user interface 506 which mayinclude a display and a keyboard. In an embodiment, the display may be atouch panel with or without a keyboard.

Alternating magnetic field signals are received, under the control ofthe processing unit 504, in response to the transmissions of thetransmitter-receiver 500 from the object 502 by the transmitter-receiver500 which has a plurality of the components 10 as detectors with thesuperconducting junctions 102 in a cryostatic temperature range. Thealternating magnetic field signals detected using the superconductingjunctions 102 may be used to form an image of the object 502 and theimage may be used to diagnose a variety of good or bad conditions of theobject 502. Often the object 502 is the brain and/or a part of a spinalcord. Still, whole body or some other body part of a person or animalmay be scanned with the MRI machine.

The processing unit 504 may control the heater 400 of the temperaturecontrolling element 200 to heat the superconducting junctions 102 of thetransmitter-receiver 500 into a non-superconducting state before, at orafter the at least one magnetic pulse of one measurement output by thetransmitter-receiver 500. The processing unit 504 may control the heater400 of the temperature controlling element 200 to stop heating after themagnetic pulses output by the transmitter-receiver 500. That is, eachsuperconducting junction 102 is in the non-superconducting state betweenthe at least one magnetic pulse of one measurement and the detection,where the detection is based on or performed after said at least onemagnetic pulse using the at least one superconducting junction 100.Additionally, the heater 400 stops heating the at least onesuperconducting junction 100 before the detection for allowing the atleast one superconducting junction 100 return to the superconductingstate for the detection.

The structures around the superconducting junctions 102 are constantlyin a temperature range where the first and second layers 104, 106 wouldbe superconducting, because the heater 400 heats only thesuperconducting junction 100 to a temperature associated with thenon-superconducting state. The structures around the superconductingjunctions 102 are also constantly cooled by the cooling system 402 whichkeeps the directly adjacent surroundings of each of the superconductingjunctions 102 in a temperature range below the threshold between thesuperconducting state and the non-superconducting state of the first andsecond layers 104, 106. When the heater 400 stops producing heat, thefirst and second layers 104, 106 and the whole superconducting junction100 cool quickly and reach the superconducting state fast for enablingdetection of the alternating magnetic fields coming from the body part502 by each of the superconducting junctions 102. The change fromnon-superconducting state to the superconducting state is quicker thanin the prior art, because the volume of the first and second layers 104,106 and the whole superconducting junction 100 is small compared towhole component 10, and because the heat of each of the superconductingjunctions 102 produced by the heater 400 is quickly absorbed by thecolder surroundings and the cooling system 402.

FIG. 6 illustrates another example of the magnetoencephalography (MEG)machine. The MEG machine may be based on SQUID (Superconducting QuantumInterference Device). The measuring part 600 comprises a plurality ofthe superconducting junctions 100 for detecting magnetic fields of theobject 502 such as a head with the brain. The stabilizer 300 may keepthe temperature of the plurality of superconducting junctions 100stabilized within the second temperature range 802.

The heater 400 of the temperature controlling element 200 may start orincrease heating in response to the information about the measuredtemperature which is measured with the thermometer 404 and whichdecreasing. The heater 400 of the temperature controlling element 200may stop or decrease heating in response to the information about themeasured temperature which is increasing.

FIG. 7 illustrates an example of a period of time of heating and aperiod of time in the non-conducting state of the superconductingjunction 100. The vertical axis refers to temperature and power ofheating. The horizontal axis refers to time. Both axes are in arbitraryscale. During the first period 700 the heater produces heat. Because ofa potential delay, the superconductive junction 100 is innon-superconductive state during the second period 702 in response tothe heating during the first period 700.

FIG. 8A illustrates an example of variation of temperatures of the layer102 of the non-superconducting material. The vertical axis refers totemperature. The horizontal axis refers to time. Both axes are in anarbitrary scale. The temperature of the superconducting junction 100follows the temperature of the layer 102 of the non-superconductingmaterial i.e. is in practice the same as the temperature of the layer102 of the non-superconducting material. The temperature fluctuation ofthe layer 102 of the non-superconducting material may be considered tostay in the first range 800 if the stabilizer 300 is used. In reality,the temperature fluctuation is attenuated with the stabilizer such thatthere is a high probability that the temperature is cool enough for thesuperconducting junction 100 to be in a superconducting state. Thetemperature of the stabilizer 300 may be equal to the superconductingjunction 100. However, it is also possible that no stabilizer 300 isused. Then it is enough that the layer 102 is kept in a temperaturebelow which the superconducting junction 100 is superconducting withoutpaying attention to the temperature fluctuation.

FIG. 8B illustrates examples of variation of temperatures of the layer102 of the non-superconducting material and the superconducting junction100 when the stabilizer 300 is used. The vertical axes of both diagramsrefer to temperature. The horizontal axes refer to time. The axes are inarbitrary scales. The horizontal line ST refers to a temperature belowwhich the superconducting junction 100 is superconducting and abovewhich the superconducting junction 100 is non-superconducting. Thetemperature fluctuation of the layer 102 of the non-superconductingmaterial is in the first range 800. The temperature fluctuation of thesuperconducting junction 100 is in the second range 802. The ranges 800and 802 may be the same in reality. The second range 802 of thetemperature fluctuation of the superconducting junction 100 can be keptlow with the stabilizer 300 when the superconducting junction 100 iskept in the superconducting state. When the superconducting junction 100is kept in the superconducting state by keeping the temperature belowST, it is not necessary to keep the temperature fluctuation in anyspecific range, although it may be done. By heating the SQUID into anon-superconducting state during a thermal pulse 804 it is possible toprevent the situation where the high transient magnetic field during thethermal pulse 804 causes the persistent flux traps, because the fluxtraps are only generated in a superconducting state. In a similarmanner, when the superconducting junction 100 is kept in thenon-superconducting state by keeping the temperature above ST, it is notnecessary to keep the temperature fluctuation in any specific range,although it may be done.

FIG. 9 illustrates a measurement of a hysteresis curve of thesuperconducting junction 100 in liquid helium. The vertical axis denotesvoltage over the superconducting junction 100 and the horizontal axisdenotes current through the superconducting junction 100.

FIG. 10 illustrates an example of the processing unit 504 which maycomprise one or more processors 1000 and one or more memories 1002including a computer program code. The one or more memories 1002 and thecomputer program code configured to, with the one or more processors1000, cause the apparatus at least to control the heater 400 to heat andstop heating.

In an embodiment, the one or more memories 1002 and the computer programcode may, with the one or more processors 1000, cause apparatus at leastto control the heater 400 on the basis of the information about thetemperature measured by the thermometer 404.

In low-field MRI, the SQUID can be protected by heating everysuperconducting junction 100 into a non-superconducting state, and stillobtain fast recovery back to the superconducting state.

The superconducting junctions 102 may be applied in medical low-fieldMRI or where-ever low-frequency noise in Josephson junctions causesproblems. Possible applications may be related tomagnetoencephalography, magnetotellurics in ore prospecting, quantuminformation processing, gain stabilization for detector-readoutamplifiers.

FIG. 11 is a flow chart of the manufacturing method. In step 1100, alayer 102 of thermally conducting, non-superconducting material isformed between a first layer 104 and a second layer 106 of thesuperconducting material, the non-superconducting layer 102 being incontact with either the first layer 104 or the second layer 106 ofsuperconducting material. In step 1104, a tunneling layer 108 ofinsulating material is formed between the first layer 104 and the secondlayer 106 of the superconducting material.

FIG. 11 illustrates more detailed manufacturing steps. In step 1100, thelayer 102 of non-superconducting and thermally conducting material witha superconducting proximity effect may be formed between the first layer104 of superconducting material and the second layer 106 ofsuperconducting material.

In step 1102, the first layer 104 of superconducting material and secondlayer 106 of superconducting material may be overlapped with each otherat a superconducting junction 100, the first layer 104 ofsuperconducting material and second layer 106 of superconductingmaterial providing electric contacts the superconducting junction 100.

In step 1106, the non-superconducting layer 102 of thenon-superconducting material may be located in contact with either ofthe first layer 104 of the superconducting material or the second layer106 of the superconducting material for allowing thermal control of thesuperconducting junction 102 with the layer 102 of non-superconductingmaterial.

When manufacturing the superconducting junction and apparatus a“trilayer” may be formed first. That is, the second layer 106 of thesuperconducting material may be covered with the tunneling layer 108.During this phase, also at least one (superconducting) layer which isnot numbered and which is beside and/or on the tunneling layer 108 maybe added (see FIG. 1A). Then the non-superconducting layer 102 of thenon-superconducting material may be formed on the tunneling layer 108.Finally, the first layer 104 of the superconducting material may beformed on the non-superconducting layer 102 of the non-superconductingmaterial.

In an alternative way, it may be possible to grow thenon-superconducting layer 102 of the non-superconducting materialdirectly on the tunneling layer 108 without the at least one unnumberedsuperconducting layer (see FIG. 1A). In a still alternative way, it maybe possible to grow the non-superconducting layer 102 of thenon-superconducting material on the second layer 106 of thesuperconducting material, and after that it may be possible to form thetunneling layer 108 thereon.

FIG. 12 is a flow chart of the control method. In step 1200, temperatureof a superconducting junction 100 is controlled by conducting heat toand/or from a superconducting junction 100 with a thermally conductivelayer 102 of non-superconducting and thermally conductive material, thelayer 102) of non-superconducting material and a tunneling layer 108 ofinsulating material being between a first layer 104 of superconductingmaterial and a second layer 106 of superconducting material.

In more detail of step 1200, temperature of a superconducting junction100 may be controlled by conducting heat to and/or from asuperconducting junction 100 with a thermally conductive layer 102 ofnon-superconducting and thermally conductive material which possesses asuperconducting proximity effect, the layer 102 of non-superconductingmaterial and a tunneling layer 108 of insulating material being betweena first layer 104 of superconducting material and a second layer 106 ofsuperconducting material which overlap each other at the superconductingjunction 100 and provide electric contacts the superconducting junction100, and the layer 102 of the non-superconducting material being incontact with either of the first layer 104 of the superconductingmaterial or the second layer 106 of the superconducting material.

The method shown in FIG. 12 may be implemented as a logic circuitsolution or computer program. The computer program may be placed on acomputer program distribution means for the distribution thereof. Thecomputer program distribution means is readable by a data processingdevice, and it encodes the computer program commands, carries out themeasurements and optionally controls the processes on the basis of themeasurements.

The computer program may be distributed using a distribution mediumwhich may be any medium readable by the controller. The medium may be aprogram storage medium, a memory, a software distribution package, or acompressed software package. In some cases, the distribution may beperformed using at least one of the following: a near fieldcommunication signal, a short distance signal, and a telecommunicationssignal.

It will be obvious to a person skilled in the art that, as technologyadvances, the inventive concept can be implemented in various ways. Theinvention and its embodiments are not limited to the example embodimentsdescribed above but may vary within the scope of the claims.

The invention claimed is:
 1. A superconducting junction comprising: afirst layer and a second layer of superconducting material; a tunnelinglayer of insulating material disposed between the first layer and thesecond layer of the superconducting material; and a layer of thermallyconducting, non-superconducting material disposed between the firstlayer and the second layer of the superconducting material, thenon-superconducting layer being in contact with either the first layeror the second layer of superconducting material; wherein the layer ofthermally conducting, non-superconducting material is configured to bethermally connected with at least one thermal conductor coupled with atemperature controlling element.
 2. The superconducting junction ofclaim 1, wherein the layer of non-superconducting material with asuperconducting proximity effect is in contact with either of the firstlayer of the superconducting material or the second layer of thesuperconducting material for thermal control of the superconductingjunction within the superconducting junction; and the first layer ofsuperconducting material and the second layer of superconductingmaterial overlapping each other at the superconducting junction andbeing configured to provide electric contacts the superconductingjunction.
 3. The superconducting junction of claim 1, wherein an area ofthe layer of the non-superconducting material within the superconductingjunction is smaller than a superconducting area of the superconductingjunction.
 4. The superconducting junction of claim 1, wherein thenon-superconducting material of the non-superconducting layer isconfigured to extend outside the superconducting junction.
 5. Thesuperconducting junction of claim 1, wherein an area of the layer of thenon-superconducting material has a different shape from an area of thelayer of the superconducting material within the junction.
 6. Thesuperconducting junction of claim 1, wherein an area of the layer of thenon-superconducting material has a shape of an annulus, so that thesuperconducting junction being configured to comprise a structure wherea central area of the superconducting junction is free from thenon-superconducting material.
 7. A method of manufacturing asuperconducting junction, the method comprising forming a layer ofthermally conducting, non-superconducting material between a first layerand a second layer of the superconducting material, thenon-superconducting layer being in contact with either the first layeror the second layer of superconducting material, the layer of thermallyconducting, non-superconducting material being thermally connectablewith at least one thermal conductor for a thermal connection with atemperature controlling element; and forming a tunneling layer ofinsulating material between the first layer and the second layer of thesuperconducting material.
 8. The method of claim 7, wherein the layer ofnon-superconducting material with a superconducting proximity effect isformed to contact with either of the first layer of the superconductingmaterial or the second layer of the superconducting material for thermalcontrol of the superconducting junction within the superconductingjunction; and the first layer of superconducting material and the secondlayer of superconducting material are formed to overlap each other atthe superconducting junction and are configured to provide electriccontacts the superconducting junction.
 9. The method of claim 7, whereinan area of the layer of the non-superconducting material within thesuperconducting junction is formed to be smaller than a superconductingarea of the superconducting junction.
 10. The method of claim 7, whereinthe non-superconducting material of the non-superconducting layer isconfigured to extend outside the superconducting junction.
 11. Themethod of claim 7, wherein an area of the layer of thenon-superconducting material is formed to have a different shape from anarea of the layer of the superconducting material within the junction.12. The method of claim 7, wherein an area of the layer of thenon-superconducting material is formed to have a shape of an annulus, sothat the superconducting junction is configured to comprise a structurewhere a central area of the superconducting junction is free from thenon-superconducting material.